Every now and then we see people worrying about their carbon fibre parts, and it struck me that I don't know how thick the various tubes are.

eg Carbon Fibre fork leg – how thick would that be? I've never seen a broken one.

Some are thick, some are thin…

My road forks which snapped (when I stuffed them into a car at 35mph) were a bit less than 2mm thick I reckon, they failed roughly inline with the brake pads on both legs.

Look at seatposts, cheap ones are often really thick, whilst some crazy ones like AX-lightness are about 0.5mm, like this one:

My Syncros Factory FL seatpost is about 3.5mm thick.

Generally quite thin compared to metal but it depends on the location entirely, it's not very good at compressive loads so requires more meat at those points and so can be much thicker than metal in those spots. I have a broken carbon crank arm I will pop a photo up of, it's only ~0.5mm.

http://www.bustedcarbon.com/

coffeeking – Member
Generally quite thin compared to metal

Eh? steel can be 0.5mm no problem!

I think he means quite thin compared to a piece of metal of equivalent tensile strength/stiffness.

Can someone set up http://www.bustedalu.com and http://www.bustedsteel.com for some ballance?

Most of those stories seem to be I rode into the back of a truck at 30mph and my bike snapped.

It would be good to know the actual thickness of the tubes.

What would that information give you epicyclo?

Just for comparison's sake. eg if all the bits failing are 1mm and there's nothing with 2mm it may suggest which bits are stronger.

Of course maybe the real question is which factory did the item come from (not the brand).

Euler buckling

I am guessing manufacturers would have accomodated 2mm carbon into their designs if thinner carbon always snapped.

It gets about 3 million times more complicated than how thick the tube wall thickness is..

Tha layup of the mat, the weave, and the fibre dia, direction of the fibres, are all variable giving infinite tuning for even a simple round tube, also probably a few differnt resins, curing techniqes, times, temps…

The thickness and the failure rate are incredibly unlikely to have any correlation! I'd go so far as saying that it's irrelevant.

If a structure is not strong enough then an extra 1 or 2mm can make a difference.
But, if a material has poor fracture toughness, and fractures can travel at the speed of sound (for that material); then what difference does an extra 1 or 2mm make?
Fracture toughness can be more important than tensile strength to avoid structural / material failure.

CFRP Carbon Fibre Reinforced Plastic is poor in compression.
In a similar way that rope is good for pulling but poor for pushing.

I realise strong carbon fibre products can be made paper thin.

It occurred to me that many carbon forks are made out of tubes which are commercially available. From the sound of those I've flicked with my fingernail, they are not made from thin material.

So does anyone know the actual thickness used in carbon forks (the common round tubed ones)?

They vary. That's like saying 'how thick are the walls of a 27.2mm seatpost', or how thick's the top tube of a hardtail frame. Otherwise every single fork would likely weigh the same!

Ok, let me rephrase the question. I know there are different thicknesses, I just want some examples.

Does anyone actually know what thickness a particular fork is? eg On-One, Pace

Not opinion, or why there's different thicknesses, but just the fact.